Passive screw locking mechanism

Abstract

Methods and devices are provided for passively locking a bone screw within a bone plate. In particular, the methods and devices allow a bone screw to be locked within a thru-hole in a bone plate without requiring any additional locking steps. In an exemplary embodiment, an annular feature is provided in a thru-hole of a bone plate, or in a bushing that is disposed within a thru-hole of a bone plate, for engaging a bone screw. The annular feature can be configured such that it allows the bone screw to be inserted through the thru-hole at various insertion angles while still being effective to prevent back-out of the bone screw, thereby locking the screw to the plate.

What is claimed is: 
     
       1. A method for locking a bone screw within a plate, comprising:
 positioning a plate having a thru-hole on a bone surface, the thru-hole including a bushing disposed therein and having an annular feature formed on an internal surface thereof; and 
 inserting a bone screw through the bushing and into bone, threads on the bone screw engaging the annular feature as the bone screw is inserted through the bushing, and the annular feature abutting a proximal-most surface of the threads on the threaded shaft when the threaded shaft is threaded through the thru-hole; 
 wherein the annular feature resides in a single plane such that the bone screw can be inserted through the hushing at various insertion angles relative to an axis of the thru-hole. 
 
     
     
       2. The method of  claim 1 , wherein the annular feature engages an annular groove formed between a head and the threads of the bone screw. 
     
     
       3. The method of  claim 1 , wherein the bushing is a split hushing. 
     
     
       4. The method of  claim 1 , wherein the bushing is polyaxially rotatable within the thru-hole in the plate. 
     
     
       5. The method of  claim 1 , wherein the bone screw includes a head that is received within the bushing. 
     
     
       6. The method of  claim 1 , wherein the annular feature engages an annular groove formed between the threads and the head of the hone screw when the head is seated within the bushing. 
     
     
       7. The method of  claim 1 , wherein the threads have a major diameter that is greater than an inner diameter of the annular feature, and the threaded shank has a minor diameter that is less than an inner diameter of the annular feature. 
     
     
       8. The method of  claim 1 , wherein the annular feature comprises an annular flange disposed around the internal surface of the bushing. 
     
     
       9. The method of  claim 1 , wherein the annular feature comprises a plurality of tabs spaced annularly around the internal surface of the bushing.